The present invention relates to an improvement in an ink jet system printer of the charge amplitude controlling type.
In an ink jet system printer of the charge amplitude controlling type, wherein ink drops charged with charging signals are electrostatically deflected in accordance with the charge amplitude thereon as they pass through a high-voltage electric field thereby printing desired symbols such as alphabet characters, it is of importance that the application of the charging signals or the phase of the charging signals is timed to be in agreement with the ink drop separation rhythm. To this end, one approach has been proposed, wherein detection signals are formed and applied to a charging electrode which also receives the charging signals in order to detect the amplitude of charge on ink drops attributable to phase detection and, as a result, the charging signals are compensatively phase-controlled to be accurately synchronous with the ink drop formation rhythm. This approach has been disclosed in detail in our co-pending application Ser. No. 434,218, now abandoned, entitled "PHASE SYNCHRONIZATION FOR INK JET SYSTEM PRINTER", filed on Jan. 17, 1974.
One manner of detecting the charge amplitude is to establish a wire electrode closely adjacent to a beam gutter for recovery of waste ink drops not attributable to printing, the phase detecting ink drops striking directly against the wire electrode. However, since the electrically conductive ink liquid adheres to the electrode, there is a possibility of shunting the charge amplitude detecting electrode due to the ink liquid, which would exhibit a high impedance, and hence create a problem with respect to reliability. In addition, since the detecting electrode is positioned behind a pair of high voltage deflection plates and adjacent the beam gutter, the period required for the phase detecting ink drops to arrive at the charge amplitude detecting electrode after application of the phase detecting signals is comparatively long, for example, several milliseconds. This provides a time delay in phase correction.
Accordingly, it is an object of the present invention to provide a charge amplitude detection unit which exhibits high reliability and high response velocity.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objective, the device of the present invention has been developed to function to detect the charge amplitude on ink drops by virtue of electrostatic induction, wherein a detecting electrode with a strip or panel shape is provided adjacent the wake of the ink drops. Since the present arrangement detects the charge amplitude due to electrostatic induction without being actually in physical contact with the ink drops to be detected, the surface of the detecting electrode may be held in an optimum state at all times to ensure correct measurements. Moreover, since the present arrangement in no way interferes with the path of the ink drops, the detecting electrode may be positioned very closely behind a charging electrode to increase a response speed.